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Biomedical subjects

B Kanyár

Publications and source records attributed to B Kanyár.

At least 19 recordsLinked to original sources
PubMed2002

Concentration of 226Ra in Hungarian bottled mineral water.

Concentration of the radionuclide 226Ra was determined in almost every type of bottled mineral water commercially available in Hungary. Determination of the radon coming from the radium dissolved in the water was used for activity measurement. As the results show, the 226Ra concentrations exceed the level of 100 mBq l(-1) in six cases out of the 28 types of mineral water investigated. In one case 3 Bq l(-1) was measured, which provides 0.3 mSv year(-1) committed effective dose for adults in the case of a consumption rate of 1 l day(-1). In soft drinks produced from mineral water a concentration of 2.6 Bq l(-1) was determined, which means 1.4 mSv year(-1) effective dose in the age group 12-17 years in the case of permanent daily drinking of 1 l of these beverages.

Adolescent↗
PubMed2001

Determination and use of the monetary values of the averted person-sievert for use in radiation protection decisions in Hungary.

The monetary value of the averted dose is a key element in the implementation of the optimization principle both in radiation praxis and intervention. The main concept of this principle is to select options so as to maintain exposures at a reasonable level. The feature of this concept is to look for the minimal total cost, i.e., the sum of the costs of protection and health detriment. In its publications, ICRP emphasized the need for developing models which also take into account the "subjective" aspects of health detriment in the optimization process, such as the perception of risk by individuals and the need to put more emphasis on equity in the distribution of individual doses. This paper proposes a modified alpha-value model based on CEPN's model (Centre d'Etude sur L'Evaluation de la Protection dans le Domaine Nucleaire) to put more emphasis on recently published considerations about the smaller effects of the portion of collective dose derived from small doses. The parameters of the monetary value of unit collective dose averted, which is a key element of this type of model, can be estimated by means of approaches like human capital (HC) and willingness to pay (WTP) from the point of view of economic theories. The present study summarizes the results achieved by WTP among the radiation specialists mainly from the Paks Nuclear Power Plant, Hungary. The aim of the effort was to determine the value of a statistical life and the monetary value of a unit person-sievert associated with averted occupational exposure due to ionizing radiation. To apply the WTP method, a questionnaire has been prepared on the basis of the one introduced by CEPN in the late 1990's. The investigations show that the value of US$6,200 person-Sv(-1) seems to be acceptable for the alphabase-value for the occupational situation in Hungary in 1999. WTP assessments should be applied with caution since the economic level of the country, the workplace surveyed, and the computational methods affect the results. In addition, achieving a high level safety culture must rely on international cooperation both from the theoretical and practical viewpoints, and international markets affect the associated costs. Therefore the monetary requirements cannot always be assessed solely on a national basis.

Cost-Benefit Analysis↗
PubMed1998

Radiation hazard of coal-slags as building material in Tatabánya town (Hungary).

High concentrations of 226Ra (865-2,383 Bq kg(1)) were measured in the coal-slags, originated from the region of the settlement Tatabánya, Transdanubian Middle Mountains, Hungary. These slags are commonly used as building materials in this district. The external gamma dose rate was measured in 188 rooms at different heights above the floor. In 124 rooms with slags used for construction, the average absorbed dose rate was 296 nGy h(-1). In 10 apartments the average radon concentration was 502 Bq m(-3). In that case the estimated effective dose due to inhaled radon and its progeny and gamma radiation was 10.3 mSv y(-1).

Coal↗
PubMed1988

Pharmacokinetics and toxicity of mitomycin C in rodents, given alone, in combination, or after induction of microsomal drug metabolism.

The pharmacokinetics of mitomycin (MMC) was studied in Wistar rats. Up to five half-lives, the plasma concentration-time curve was biphasic. The AUC changed linearly with increasing doses between 0.5 and 7.5 mg/kg, which corresponds to 0.2 and 3 times the LD50 value in rats. Most of the drug was metabolized, and only 1%-2% and 10%-15% of the dose was eliminated unchanged by biliary and urinary excretion, respectively. The AUC of MMC at the LD50 is slightly less than that reported for the human MTD. Inoculation of MMC together with 5-fluorouracil and doxorubicin did not change the terminal half-life of MMC but decreased the total body clearance and the volume of distribution. The lack of significant influence of phenobarbital and 3-methylcholanthrene pretreatment on the terminal elimination half-life suggests that microsomal drug-metabolizing enzymes inducible by these compounds do not play a decisive role in the in vivo biotransformation of MMC.

Animals↗
PubMed1988

The role of comparative pharmacokinetics in the planning of human dose escalation: the experience with diacetyldianhydrogalactitol.

The pharmacokinetics of diacetyldianhydrogalactitol (DADAG) was compared in mice, rats, and humans. The ratios of human therapeutic dose (ThD) to the LD10 were 8 and 5 in mice and rats, respectively. The ratios of the corresponding AUCs of DADAG were 20 and 17, whereas those of dianhydrogalactitol (DAG), the main, active metabolite of DADAG, were 8 in both species. The lower human-to-rodent ratio for DAG was due to the fact that twice as much DAG was formed in the animals. Other factors contributing to the larger AUC in man were the 3-5 times smaller distribution volume found in humans as well as the lower hexitol sensitivity of human bone marrow cells. We conclude that in addition to the distance between the AUCs of the LD10 and of the human starting dose, interspecies pharmacokinetic differences should also be considered in planning the rate of dose escalation.

Algorithms↗
PubMed1986

Pharmacokinetic study in a phase I trial with an alkylating agent, diacetyldianhydrogalactitol (DADAG).

Diacetyldianhydrogalactitol (DADAG), a new alkylating hexitol derivative, was given in 30-min infusions for 5 consecutive days or as a single high-dose administration. The parent drug was eliminated in a biphasic manner, with a terminal half-life of 30-40 h. Dianhydrogalactitol (DAG), the main, pharmacologically active metabolite, appeared after a lag time of about 0.2-0.6 h. Its peak concentration was reached 1-2 h after termination of the infusion. The terminal elimination of DAG followed that of the parent compound. During the 5-day schedule slight accumulation was observed, and the plasma concentrations of both compounds approached the steady state. Over a dose range of 75-1050 mg/m2 the daily mean plasma concentrations of DADAG increased by only about 3-4 times. Dose-dependent expansions of the distribution volumes of the drug (Vc, V lambda, Vss) were observed. The behavior of DADAG and DAG in the body could be adequately described by a three-compartment open model. After equilibration the plasma levels of the parent compound and its metabolite were determined by the rate of return of DADAG from the peripheral compartment and its conversion to DAG.

Adult↗
PubMed1986

Relation between dose, plasma concentration and toxicity in a phase I trial using high dose intermittent administration of an alkylating agent, diacetyldianhydrogalactitol (DADAG).

Diacetyldianhydrogalactitol (DADAG), a new alkylating sugar alcohol derivative, was administered as single, 30-min infusions in doses ranging from 390 to 1200 mg/m2. The dose-limiting toxicity was myelosuppression. The median times to WBC nadir and regeneration were 16 and 21 days, and to platelet nadir and recovery 20 and 27, respectively. Nausea and vomiting occurred frequently and were of moderate severity. For phase II studies 900 mg/m2 DADAG given every 4-6 weeks is recommended. The area under the plasma concentration time curve (AUC) for DADAG did not increase in proportion with dose escalation; it changed only from 235.5 +/- 70.7 to 262.4 +/- 71.5 micrograms h ml-1 between doses of 690 and 1050 mg/m2. No correlations between the dose administered and the nadir values for haemoglobin concentration, WBC and platelet counts, or the number of episodes of vomiting were demonstrable in this dose range. Such an association was revealed, however, when the above biological variables were related to the individual AUC for DADAG.

Adult↗
PubMed1986

Pharmacokinetics and metabolism of dianhydrogalactitol DAG in patients: a comparison with the human disposition of dibromodulcitol DBD.

Dianhydrogalactitol (DAG), labelled with 3H, was administered in single intravenous or oral doses to six patients (three in each group) with cancer. Kinetic parameters were calculated for the unchanged DAG and its biotransformation products. Elimination of the drug by metabolism and excretion was described by a catenary model. In order to elucidate the role of DAG as a mediator of the alkylating action of the cytostatic drug dibromodulcitol (DBD), the pharmacokinetic parameters of DAG and DBD were compared. The mean residence time for pharmacologically active molecules in the body was six times shorter for DAG (1.9 hr) than for DBD (11.4 hr). Alkylating action and metabolic degradation proceeded about 8-9 times faster for DAG than for DBD. The process of DBD alkylation implies a slow solvolytic conversion of the parent drug into the more reactive bromoepoxide and DAG. The preformed DAG would be rapidly consumed by intracellular alkylation and degradation, while unchanged DBD could form a depot in the cells and exert its cytostatic activity through the epoxides released in situ by solvolytic activation. Thus DBD entering the cells in unchanged form may have a more important role in its therapeutic effects than had been assumed earlier.

Adult↗
PubMed1981

Clinicopathological studies of liver cirrhosis and hepatocellular carcinoma in a general hospital.

Clinicopathological studies of 181 patients with liver cirrhosis undergoing autopsy in the pathology department of a municipal hospital between 1973 and 1976 are reported. The main etiological types were alcoholic (25.4 per cent), HBsAg positive (14.9 per cent), and cryptogenic cirrhosis (54.7 per cent). Four patients had multifactorial and secondary biliary cirrhosis and one patient had congestive cirrhosis. The morphological characteristics of the condition and the age and sex distribution of the patients were analyzed in each etiological group. Hepatocellular carcinoma occurred in 28.7 per cent of the cases, most frequently in association with HBsAg positive cirrhosis. Hepatocellular atypia was significantly more frequent in HBsAg positive than in other etiological types of cirrhosis and significantly more frequent in cases associated with hepatocellular carcinoma than in those not associated with it.

Aged↗
PubMed1979

Hyperaldosteronism in the sodium depleted rat: effect of a low sodium diet or diuretic treatment on steroid output by the superfused adrenal zona glomerulosa.

The effect of chronic and acute sodium depletion on the function of the adrenal zona glomerulosa was examined by means of superfusion of adrenal capsular glands. The glands were removed from rats kept on a low sodium diet for 7 days or from dexamethasone-pretreated rats 30 min after administration of the diuretic drug furosemide. Chronic sodium depletion brought about a high initial output of aldosterone followed by a rapid fall in output. The initial rate of corticosterone output did not differ significantly from that by control glands but exhibited a more rapid decline with time. Aldosterone: corticosterone ratio, an indicator of the rate of conversion of corticosterone to aldosterone, was much higher in the sodium depleted group throughout the whole superfusion period. Acute sodium depletion was followed by high initial and rapidly falling aldosterone and corticosterone output, without any significant change in the ratio of aldosterone to corticosterone output rate. The above dynamic patterns of steroid output indicate that a sodium deficient diet evokes hyperaldosteronism by increasing the formation of aldosterone from corticosterone (not excluding the possibility of increasing the formation of corticosterone as well) while diuretic treatment stimulates aldosterone secretion by acting on the formation of corticosterone only.

Adrenal Cortex↗
PubMed1978

Program to estimate parameters of linear systems without numerical differentiation.

This paper describes a computer program for estimating the parameters of a linear differential equation systen with constant coefficients by use of a nonlinear least-squares method. For minimization the sum of squares of an existing standard program, the Gauss-Newton gradient procedure, is employed. The differential equation system is solved by the Taylor expansion method. The advantage of this approach is that the derivatives with respect to the parameters are available without numerical differentiation. Therefore the inaccuracy inherent in numerical differentiation and the problem of choosing the modification of the parameters are eliminated. The given procedure is applicable for all the first order gradient methods. The presented method was tested with generated data from a four-compartmental model.

Computers↗
PubMed1978

Parameter sensitivity analysis for designing experiments in kinetics.

For the Michaelis-Menten binding kinetics and for a two- and a three-compartmental model a parameter sensitivity analysis is performed to design experiments. According to the mathematical results in the case of the binding kinetics the substrate concentrations s approximately Km are optimal in view to the variance of the Michaelis constant Km. In the case of the two-compartment model the results of the calculations are tested by the use of computer-simulated data. The correspondence between the sensitivity and simulation results is satisfactory.

Computers↗